This standard specifies the type, size, technical conditions and marks of hexagon head bolts with fine threads. This standard is applicable to thread nominal diameter d = 8 mm ~ 64 mm, fine thread, performance class 5.6, 8.8, 10.9, A2-70, A4-70, A2-50, A4-50, CU2, CU3 and AL4 , Hex head bolts with product grades of A and B. Class A is used for d=8 mm~24 mm and l≤10d or l≤150 mm (according to the smaller value); Class B is used for d>24 mm or l>10d or l>150 mm (according to the smaller value) bolts. Coarse thread bolts specified in GB/T 5782 should be preferred.